The purpose of this study is to provide information about the mode of operation of the contractile apparatus of skeletal muscle by measurements of its viscoelastic properties. Muscle models will be constructed based on the results of the experiments, and the passive and active nature of the elements of the mode identified. Additional measurements will verify whether or not the model is applicable to unit sarcomere behavior. Information about the rate and extent of crossbridge attachment and detachment will also be sought. In the coming year we plan the following: (1) to verify the uniformity of strain along the test specimen in response to imposed strains at the tendons; (2) to perfect the single fiber dissection; (3) to measure the dynamic and static mechanical characteristics on these fibers and muscle bundles at rest and during tetanic activation, and to complete the whole muscle study by obtaining the tetanic measurements; (4) to examine the fine structure patterns of the lst order laser diffraction line using rapid analog processing. We expect that our unique method of measuring the macro-mechanical propertes of frog skeletal muscle will contribute to a fuller understanding of mammalian skeletal and cardiac muscle behavior at the level of the sarcomere.